Production of light concrete bodies



. Gross Referee Examiner COATING OR PLASTKC Li, 9'3 Minted 4 a 2 7' 2,226,348

UNITED STATES PATENTOFIFICE Josef Baab, Stuttgart-Bad Cannstatt, Germany No Drawing. Application May 19, 1937, Serial No. 143,621. In Germany September 19, 1936 2 Claims. (01.10 f

'It has hitherto not been possible to make pumice high'and uneconomicai quantities of heat would concrete or any similar light concrete having a be required, but the heat content of the saturating porous structure with suflicient compressive binding agent is used. With this object in view, strength for the purposes of road-making or the the concrete bodies are saturated with the binding .like, as the porous structure of the grain of light agent under a pressure of at least 3 atmospheres 5 material, for instance of the grain of pumice, above the saturation pressure of the water vapour,

.; collapses under any considerable loads. In spite corresponding to the temperature of the binding of the low weight of paving blocks of light concrete, agent, whereupon the pressure is lowered for a which is of prime importance for the roadways short period below the said saturating pressure of bridges, and in spite of the excellent grip proand is then restored again. The pressure drop 10 vided by a road surface of light concrete and its varies according to the density of the concrete very great freedom from ice formation, its adopand the size of the pumice grain and can be ascertion in practice for road-making purposes has tained by the expert without difliculty through therefore not been possible. The grain of pumice experiments. the one hand it must not be or like is ground to powder and corresponding too high, so that whole grain as it were ex- 1 openings or depressions remain, which result in plodes, while on e other hand it must not be too a rapid further destruction of the light concrete low, because of the pressure floss in the pores of body. the concrete body. It may be of advantage in This applies both in cases where the light 0011- some cases, for instance in the case of a coarse crete is made simply in the usual way of granupumice grain, to repeat this process several times.

lated pumice or similar light grains of porous The efiect of this procedure is as follows: structure and cement or the like, with or without in the first place, the binding agent is in a the additional use of other suitable added maknown manner forced into the pores of the conterials, and in cases in which, as has been already crete body, which is bound with cement or the like, i 5 suggested, pumice concrete bodies are treated first and is brought to the concrete grains, being heated 25 in a vacuum and then under pressure with hot tar in this way through the pressure employed. The or bitumen. Moreover, these saturating subwater contained in the cavities of the pumice stances cannot penetrate into the grain of pumice. grains is thus caused partly to evaporate and the The invention is based on the recognition of the saturated water vapour produced presses from fact, that in order to enable natural or artificial within against the walls of the pore with the sat- 30 urnice or equivalent substances vmg a porous uration pressure corresponding to its temperature. Etfi''tfire to be used in the form of concrete The pressure which acts from the outside and bodies (blocks, slabs or other shapes) the cavities which lies above the saturation pressure prevents of the light grains, such as pumice grains, w the cavities from being burst open by the internal i geclgse djnthemselves, must be opened wi hout vapour pressure, so that in this state of equilibrium 35 I" destroying the coherence and the characteristic a thorough heating of all the pumice grains right 1 structure of the grain, so that the hot saturating into the core is brought about. Through the low- E a ent, such as tar, bitumen or the e can peneering of the external pressure, which is preferably trate into the'i'h'teri'or of the grain and throug brought a o u n e S urated water the filling out of the cavities a suitable compresvapour contained in the cavities bursts the wall 40 sion strength and at the same time a rigid of the particular cavity at the weakest place and anchoring of the grain in the shaped body reopens for itself a path into the atmosphere. The sults. In this way a pumice concrete body of water vapour produced by the re-evaporation of great strength to resist pressure and wear may be the water, owing to the sudden drop in pressure, obtained, which is highly suitable for road-making also flows away in this manner. The vapour bub- 45 purposes. bles rise to the surface of the fluid bitumen or the The invention consists in this, that the cavities lik nd the Vapour -D 0n the Pressure oLthe light grainare burst open by watem" bein Iiih binding agent is then case of nature piiifiicbrthe-watercuntahid n forced into the now open cavities which are thereit or in the case iwalmge or simflar by converted into pores and completely fills these 50 light grains, (frothed blast-furnace sla from iron p res- The low ing and re-establishing of the works) by artificiafiy introduced water. The Pressure may have to be repeated several times water converted for this purpose into vapour form until all the water has left the cavities and an is however not vaporized by heating, for instance intimate binding between the binding agent and in a drying drum, as for this purpose extremely the wall of the pores can take place. 55

The pressure is suitably produced by air forced in over the surface of the fluid saturating and binding agent.

According to the length of time. during which the pressure is lowered, and according to the amount of effective pressure drop more or less water vapour will escape, (that is to say remaining water is used up). If however this removal of the water by the drop in pressure during the saturation be not carried to the extreme, that is up to complete removal of the water, the water still remaining may be used for shortening and cooling the blocks.

If for instance, the pressure be lowered to such an extent and for so long that for instance 75% of the residual water is evaporated, then the cavities will become filled to about 75% with bitumen in the next pressure period. Even such a road covering may have suflicient resistance, according to the amount of traflic. Owing to the smaller absorption of bitumen, in other words owing to a small part of the cavities remaining, the weight per unit of volume will be reduced (means for varying the weight per unit volume). If, thereupon, after thorough saturation, that is at the end of the working process, the saturating material be removed out of the drum, the high pressure and the temperature in the drum being maintained, and after the removal of the saturating agent the air pressure be then lowered to atmospheric pressure, the residual water (that is the remaining is converted into vapour and forces a portion of the superfluous bitumen out of the bodies again, more particularly at the outer surface. (Advantage: the bodies will no longer be sticky to the touch. Shortening.) At the same time the vapour withdraws the heat of evaporation from the saturated bodies, whereby the latter are cooled, so that they can be sooner packed for transport.

i pumice grains for a time under water.

sorption of water can be accelerated for instance As already stated above, natural pumice, owing to its having been deposited thousands of years ago, of itself already has the necessary moisture within the cavities for enabling the process according to the invention to be carried out. In the case of artificially produced substances having a porous structure, such as frothed blast-furnace slag from iron works, termed artificial pumice, this moisture in the porous cavities is normally too small. According to the invention it has therefore to be increased ii necessary by keeping the The abby employing pressure. For this purpose the artificial pumice must be placed in a drum with water under pressure.

What I claim is:

1. A method of producing light concrete bodies irom granulated pumic and a binding agent consisting in saturating the said bodies with a hot bitumi mkImm atin ent under a pressure rosp eres above the saturation pressure of water vapour, corresponding to the temperature of the bituminous impregnating agent, reducing the pressure for a short period below the said saturation pressure and thereupon restoring the pressure again.

2. A method of producing light concrete bodies from granulated pumice and cement, consisting in saturating the said bodies with a hot bituminous impregnating agent under a pressure of at least 3 atmospheres above the saturation pressure of water vapour, corresponding to the temperature of the bituminous impregnating agent, reducing the pressure for a short period below the said saturation pressure and thereupon restoring the pressure again.

JOSEF RAAB. 

